Steer-by-wire for the chassis of the future

ZF is developing a steer-by-wire actuator in the UK that is at the heart of its move to autonomous driving.

The steer by wire technology is being developed at ZF’s engineering centre in Birmingham, UK, and the company has been showing designs for stowable steering wheels. These would be used in SAE Level 4 automated driving, where the steering wheel, or ‘handwheel actuator’, folds up and retreats into the dashboard to provide more space in the vehicle.  

The site is the result of the acquisitions of Lucas and TRW Automotive over the last decade and is the global engineering centre for steer-by-wire technology.

“There’s a huge amount of change in the industry for how you provide the control for that chassis of the future, from the electrical/electronic architecture, software defined vehicles (SDV) and autonomous driving,” said Bal Panaser, technical vice president and global manager for chassis electronics at ZF (left) . “SDV is one of the key areas where a lot of change will come through, and that’s where a lot of the new OEMs can make huge strides, that has changed dramatically.”

Rather than using a centralised controller, ZF has implemented the control algorithms in its forst pure software product, called cubiX, which runs on the electronic control unit of the actuator. The technology will be in series production next year for steer by wire systems.

“We have various ECUs from an ADAS controller to an actuator microcontroller and we can also go onto OEM ECUs. We have not yet met an OEM where we were restricted in what we can do,” he said. “We are developing more efficient control algorithms to reduce the resource demands. We already run model predictive control on existing Infineon microchips on an existing platform and we did not need to enhance the hardware.”

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The actuators have dual lanes and dual power rails for ASIL-D redundancy and works with other sensors on the chassis.

“With integrated control and networks we are now seeing we already have layers of redundancy in the sensor network that are overdimensioned and we can save cost through not only smart use of existing sensors but also by using sensors to create an emulated sensor, deriving information about the vehicle which mean we do not need a direct sensor,” said Alan Schmidt, Manager of customer engineering vehicle control at ZF.

“What by wire systems enables us to do is build a system that is close to the conventional and that is very different in different regions.”

This is used for different functions in the same ECU, for example varying the steering ratio to make parking easier, or monitoring the handwheel to interpret the driver intent with targeted feedback to the driver. Different steering modes can provide a tighter turning circle and reduced braking distances.

“We are expecting large market demand for this,” he said.

The cubiX platform was first deployed in the Lotus Eletre at the end of 2022.

“CubiX is agnostic for any actuator constellation so we can control third party actuators in the chassis,” said Schmidt. “The Eletre has a XF powertrain and front actuator but the rear steering came from a third party and cubiX had control to some degree over all these actuators,” said Schmidt.  

Cubix also has a ‘feature pack’ for autonomous driving (AD). This allows interaction with a centralised AD planning controller as well as an ADAS controller which abstracts the kinematics to control a trajectory independent of whether the vehicle has a specific actuator. For example this could be an autonomous parking feature where the ADAS system would have to be specifically tuned for vehicles with rear wheel steering or without. CubiX can detect the type of vehicle and calculate the trajectory and constraints for the controller, providing cost savings, says Schmidt.

“Cubix is independent hardware so it can be used on any automotive ECU,” he said. “We have used this on domain controllers and actuator ECUs – we just need a compute platform and networking to the chassis for sensor data and actuator control.”  

The software is not just about the steer-by-wire actuator systems. ZF is also working with tyre Goodyear to add detection algorithms to cubiX to make the tyre a sensor for the vehicle, for example to identify aquaplaning and instruct the chassis actuators to apply corrective measures, stabilising the vehicle. A “Trailer Stability Assist” function in the software can also be used to minimise a caravan snaking. 

ZF has fitted the steer-by-wire actuator and ECU with cubiX to an electric VW id.3 as a demonstration vehicle. Different setting for the steering can be applied form the central console in the car to highlight the different modes of operation.

 Beyond passenger cars, cubiX is now being developed for commercial vehicle applications where autonomy can be more easily deployed. The added safety and precision control offered by cubiX is enabling more automation in trials in a port freight yard in Germany. 

“By taking care of this complex motion control, OEMs can focus on their core competencies, defining the overall vehicle experience and perception,” said Panaser. “cubiX opens up new and efficient ways to bring enhanced safety and driver assistance features now and into the future.”